Chapter 7. The Framework Class Library

The Framework Class Library provides a cohesive set of managed types that provides the developer's view of the .NET Framework. This group of libraries serves as the runtime type libraries for many of the languages that target the Common Language Runtime. As such, the libraries must satisfy a diverse set of needs unique to the individual languages while still supporting interoperability across languages. The Framework Class Library is integral to the .NET Framework security model in that it provides encapsulation of privileged operations (such as access to the file system) in a restricted way so that code that comes from a semi-trusted ^[1] source can access the resource in a controlled manner. The libraries also provide a high level of abstraction for building applications; they are designed to help developers be more productive.

^[1] Traditionally code has either been trusted, and thereby permitted to execute, or not. Semi-trusted code is allowed to execute but the execution environment may be both restricted and monitored to prevent code from damaging resources.

Figure 7.1 provides an architectural diagram of the .NET Framework libraries. At the lowest level is the Base Framework, also known as the Base Class Library (BCL), which exposes fundamental system services. Built on top of the BCL are the XML and data support services, which are used ubiquitously in applications that target the framework to access data in XML format or from a database. At the top are the primary application models offered by the framework: ASP.NET, shown in the System.Web namespace, and Windows Forms, shown in the System.Windows.Forms and System.Drawing namespaces. ASP.NET provides both Web Forms (HTML-based functionality for thin clients, such as browsers) and Web Services (XML-based functionality for other applications).